JPH09306880A - Silicon polishing liquid composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To notably cut down the consumption of colloidal silica acting as a polishing abrasive grain by a method wherein the composition is composed of an alkalic soil suspension having PH within a specific value range receptively containing water soluble silicate component, colloidal silica and alkalic component. SOLUTION: The component is composed of an alkalic soil suspension in PH of 8.5-13 receptively containing water soluble silicate component, colloidal silica and alkalic component. In this polishing liquid composition, the practical content of the silicate component is about 0.05-5 weight% in conversion of SiO2 . Besides, the colloidal silica is effective even if its content is reduced down to 0.005-5 weight% in conversion of SiO2 . Furthermore, as for the alkalic component, alkali hydroxide, alkali carbonate, ammonium, hydrazine, organic amine, etc., are applicable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention polishes the surface of a silicon wafer for semiconductors or the surface of a film made of silicon (hereinafter, may be represented by "silicon wafer") formed on the silicon wafer. The present invention relates to a polishing liquid composition that is useful for

[0002]

2. Description of the Related Art Alkaline colloidal silica prepared by suspending silica particles as abrasive grains in an alkaline solution has been widely used as a polishing solution for polishing the surface of a silicon wafer for semiconductors. It is not clear when silica particles have come to be used as the abrasive grains of such a polishing liquid, but in Japanese Patent Publication No. Sho 49-13665, silica sol (colloidal silica) is already used for obtaining a highly precise mirror surface. Have been shown to be suitable abrasives.

"Machine and Tools" (August 1984 issue,
38-46, Toshiro Karaki), for polishing silicon wafers for semiconductors, an alkaline colloidal silica polishing liquid in which silica fine particles are suspended in an alkaline aqueous solution and a wet artificial leather polisher are used. Chemical mechanical polishing (mechanochemical polishing) is common, and this polishing method combines the mechanical polishing action of silica fine particles and the chemical polishing action of an alkaline liquid, resulting in extremely excellent smoothness and crystallinity. It has been shown that it has a characteristic that a mirror surface having good properties can be obtained.

As the alkali component used in the mechanochemical polishing, alkali hydroxide, ammonia, organic amine and the like are generally used alone or in combination of two or more kinds, and these are used as they are or salts. Is added and dissolved in the polishing liquid in the form of. The pH of the polishing liquid is generally adjusted to about 9 to 12, and solid particles such as silica particles and quartz particles having a particle diameter of about 5 to 300 nm are used as the polishing abrasive particles. It is used as a polishing liquid in a state of containing about%.

Under these circumstances, various techniques relating to polishing liquids have been proposed in recent years. As such technology,
(1) An abrasive containing a nonionic surfactant having an HLB value of 13 or more and less than 20 for the purpose of obtaining a wafer surface without haze (cloudiness) (JP-A-4-291722),
(2) For the purpose of preventing bacterial growth in the abrasive slurry, an abrasive prepared by adding a bactericide to colloidal silica (JP-A-3-202269), (3) for the purpose of further improving surface smoothness, Abrasive prepared by adding water-soluble polymer or water-soluble salt to a polishing liquid composed of silica particles and water (JP-A-4-634).
No. 28) and various other techniques are known. However, all of these techniques include solid fine particles such as silica particles and quartz particles as abrasive grains, as in the above-mentioned techniques.

Prior to these techniques, polishing liquids using only solid fine particles such as zirconia particles and alumina particles as abrasive grains have been reported. However, most of the polishing liquids known in recent years are abrasive. This is an application of mechanochemical polishing that combines a mechanical polishing action by solid fine particles that are grains and a chemical polishing action by an alkali component.
Such mechanochemical polishing is adopted as a technique capable of meeting the demands of high processing speed, excellent surface smoothness and flatness, and low processing strain.

On the other hand, as another polishing method for a silicon wafer in which no processing strain occurs, a chemical polishing method using an alkaline aqueous solution containing substantially no abrasive grains as a polishing solution is well known, but a simple chemical method is used. There is a drawback in that the shape accuracy of the polished surface is poor only by polishing. As a method of compensating for such drawbacks, a disk-type chemical polishing method has been proposed in which a flat disk-shaped soft polisher (polishing cloth or the like) or a pad is rubbed only with a chemical solution (polishing solution) (for example, “lubrication”). Vol. 33, No. 4, pp. 253-259,
Toshiro Doi). However, this polishing method has a lower polishing rate as compared with the above-described mechanochemical polishing using alkaline colloidal silica as a polishing liquid, and in reality, it cannot be effectively applied to the polishing of silicon wafers.

[0008]

As described above, conventional polishing liquids for silicon wafers generally use mechanochemical polishing that combines a mechanical polishing action by abrasive grains and a chemical polishing action by an alkaline component. The solid fine particles typified by silica particles having a particle diameter of about 5 to 300 nm are included as abrasive grains. For this reason, a large amount of abrasive grains adhere to and remain on the surface of the silicon wafer after polishing, and cleaning and removal thereof are major obstacles to the process. In particular, in recent years, when the density of semiconductor elements is increasing, even a very small amount of abrasive grains has a great influence on the performance of semiconductor elements, and if cleaning or removal is insufficient, it causes a big problem. there is a possibility.

When abrasive particles are brought into the cleaning equipment,
There is a new problem that the working environment and the equipment are contaminated, the life of the cleaning liquid is shortened, and their management becomes complicated. Not only that, but since the abrasive grains dispersed in the polishing liquid are separated / precipitated or secondary aggregated in the polishing liquid, there is a problem in that the storage and management of the polishing liquid also takes time. Moreover, the abrasive grains having a large particle size due to secondary aggregation may cause flaws on the polishing surface during polishing, and the polishing liquid may not be able to achieve its basic function.

In contrast to the mechanochemical polishing method, the above-mentioned disk-type chemical polishing method does not substantially contain abrasive grains in the polishing liquid, so that various problems caused by the above-described adhesion and retention of abrasive grains are caused. It is expected as a powerful way to avoid. However, even if this method is carried out, at present, no effective polishing liquid has been found for silicon wafers, and chemical polishing with a conventional polishing liquid is more effective than mechanochemical polishing with an alkaline colloidal silica polishing liquid. It has the decisive drawback of being slow and impractical.

The present invention has been made under these circumstances, and its purpose is to greatly reduce the use of colloidal silica acting as abrasive grains without causing the problems of the prior art. Another object of the present invention is to provide a polishing composition capable of effectively polishing the surface of a silicon wafer or the surface of a film made of silicon formed on the surface of the silicon wafer.

[0012]

Means for Solving the Problems The present invention, which has achieved the above object, means an alkaline suspension containing a water-soluble silicic acid component, colloidal silica and an alkali component, and having a pH of 8.5 to 13. It is a polishing liquid composition for silicon, which is characterized in that it is composed of

In the polishing composition of the present invention, the content of the silicic acid component is practically about 0.05 to 5% by weight in terms of SiO ₂ . The content of colloidal silica is
Even if it is reduced to 0.005 to 5% by weight in terms of SiO ₂ , the effect is exhibited. Further, examples of the alkali component include alkali hydroxide, alkali carbonate, ammonia, hydrazine, organic amine and the like, which are added or dissolved in the polishing liquid as they are or in the form of salts.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is constructed as described above, but in short, the present inventors have found that in the mechanochemical polishing process of a silicon wafer, abrasive grains, alkali components,
In the process of investigating the role of other additive components, a polishing liquid composition capable of effectively polishing the surface of a silicon wafer by coexisting a water-soluble silicic acid component and colloidal silica was found, and the present invention was completed. Although the polishing composition of the present invention is clear from the above point, it can be applied not only to polishing the silicon wafer itself but also to polishing the surface of the silicon film formed on the silicon wafer. is there. Hereinafter, the operation of the present invention will be described along with the background of the completion of the present invention.

The present inventors investigated the dependency of colloidal silica concentration on the polishing rate of silicon wafers, using an alkaline colloidal silica suspension containing sodium hydroxide and ammonia as alkaline components. As a result, in order to stably polish the silicon wafer,
If a certain concentration of colloidal silica or more is required, and by adding a water-soluble silicic acid component such as potassium silicate or sodium silicate to this alkaline colloidal silica suspension, if coexisting with colloidal silica, The inventors have found that the concentration of colloidal silica required for polishing can be reduced to 1/10 or less.

An example of investigating the dependency of colloidal silica concentration on the polishing rate of a silicon wafer is shown in FIG. In FIG. 1, ◯ and ● are polishing liquids prepared as described below (both polishing liquids have a pH of 11.0).
To 11.4), and the results of polishing under the polishing conditions shown in Example 1 below.

○: Aqueous solution of 0.2% by weight of ammonia (NH ₃ conversion), average particle diameter: 50 nm, 40% by weight of SiO ₂ conversion
A polishing liquid prepared by diluting a colloidal silica suspension containing sodium hydroxide and adjusting it to a predetermined concentration. ●; Ammonia 0.1% by weight (NH ₃ conversion), SiO ₂
0.4% by weight and 0.25% by weight of K ₂ O component
A polishing liquid prepared by diluting a colloidal silica suspension having an average particle diameter of 50 nm and containing 40% by weight of SiO ₂ and stabilized with sodium hydroxide with an aqueous solution containing the solution.

As is clear from FIG. 1, when the polishing liquid containing no water-soluble silicic acid component was used, the colloidal silica concentration (meaning “SiO ₂ concentration”, the same applies hereinafter) was 0.05.
If it is less than%, the silicon wafer cannot be polished at all, and a colloidal silica concentration of at least 0.1% by weight or more is necessary for stable polishing. Although FIG. 1 shows a representative experimental result, similar results were obtained with other combinations of alkali components and water-soluble silicates.

On the other hand, when potassium silicate was dissolved and coexisted with colloidal silica, the polishing rate could be realized practically sufficiently even if the concentration of colloidal silica was only 0.005% by weight. Of. Further, when the concentration of colloidal Syria exceeds 5% by weight, a slight increase in the polishing rate was confirmed, but at this time the viscosity of the polishing liquid increased and it became difficult to supply the polishing liquid, making it practical. lost.

Examples of the silicic acid component used in the present invention include orthosilicic acid (H ₄ SiO ₄ ) and metasilicic acid (H ₂ Si).
O ₃ ), metadisilicic acid (H ₂ Si ₂ O ₅ ), metatrisilicic acid (H ₄ Si ₃ O ₈ ), metatetrasilicic acid (H ₆ Si ₄
Any of O ₁₁ ) and the like may be used, and these may be dissolved in an alkaline aqueous solution. Alternatively, an aqueous solution containing silicates such as potassium silicate or sodium silicate added and dissolved to be contained as a silicic acid component can be used. An aqueous solution containing only can be used. Further, an aqueous solution obtained by dissolving a silicic acid hydrate in a hot alkaline aqueous solution can also be used. These silicic acids or silicates can be used alone or in combination of two or more, and the content thereof is not particularly limited, but is about 0.05 to 5% by weight in terms of SiO _2. Is practical.

On the other hand, examples of the alkali component used in the present invention include alkali hydroxide, alkali carbonate, ammonia, hydrazine and organic amine, and these can be used alone or in combination of two or more kinds. Further, these salts can be added and dissolved to form an alkaline component. When a silicate such as potassium silicate or sodium silicate is used as the above-mentioned silicic acid component, these can be used as all or part of the alkali component.

The composition of each of the alkali components is not particularly limited, but the total amount must be appropriately adjusted so that the pH of the polishing liquid is in the range of 8.5 to 13. If this pH is less than 8.5, the polishing rate will decrease and the silicic acid component in the polishing liquid will gel, making it difficult to exist as a stable aqueous solution. On the other hand, when a strong alkali having a pH of more than 13 is used, the reason for this is unclear, but strong adsorption between the pad and the wafer occurs and the force required for polishing increases. As a result, the wafer may even be damaged during polishing. Further, the chemical action becomes too strong, and the balance between the mechanical friction action and the chemical polishing action is lost, and the polishing rate is reduced.

The basic composition of the polishing composition of the present invention is as described above. From the viewpoint of imparting additional properties to the composition, a surfactant, a chelating agent, and other components are added. Can also be added. For example, an HLB value of 12 is added as an additional component to the polishing liquid having the above-mentioned basic composition.
By adding 20 or more nonionic surfactants, the affinity of the wafer surface after polishing is improved, and so-called haze of the wafer can be suppressed. Further, it is effective to add a chelating agent to the polishing liquid of the above-mentioned basic component because the metal component attached to the polishing surface can be reduced. Examples of other components include acetylacetone, glycine, pyrocatechin, ethylenediamineacetic acid and the like.

The polishing composition of the present invention can reduce the amount of colloidal silica contained in the polishing surface to 1/10 or less as compared with the conventional polishing solution which does not coexist with the water-soluble silicic acid component. It is possible to significantly reduce the adherence and residue of the colloidal silica abrasive grains. Therefore, the amount of colloidal silica as abrasive grains brought into the cleaning device after polishing can be significantly reduced, and the life of the cleaning liquid can be extended accordingly. Further, since the concentration of colloidal silica in the polishing liquid can be reduced, secondary agglomeration of colloidal silica can be suppressed, and the occurrence of polishing defects due to secondary agglomerated abrasive grains can be reduced.

The present invention will be described in more detail with reference to the following examples, but the following examples are not intended to limit the present invention, and any modification of the design of the present invention can be made without departing from the spirit of the preceding and the following. It is included in the technical scope.

[0026]

【Example】

Example 1 To 1000 cm ^{3 of} distilled water, 5 cm ³ of ammonia water containing 25 wt% of NH ₃ component was added to 10 g of an aqueous sodium silicate solution containing 37 wt% of SiO ₂ component and 18 wt% of Na ₂ O component, Furthermore, 1.3 cm ^{3 of} colloidal silica suspension containing 20% by weight of silica particles having an average particle diameter of 50 nm in terms of SiO ₂ was added, and a polishing liquid containing an alkaline sodium silicate aqueous solution containing sodium silicate and colloidal silica was added. Prepared. When the pH of the obtained polishing liquid was measured with a pH meter, it was pH = 11.6. 30 mm under the following polishing conditions using this polishing liquid
Three square Si wafers were attached to the same plate and polished. As a result, the polishing rate was 0.56 μm / mi.
n, and the smoothness of the polished surface was 0.7 nm in terms of center line average roughness (Ra). (Polishing conditions) Polishing device: Single-sided polishing machine with 12-inch plate outer diameter Pad (polishing): Polyurethane foam Polishing liquid supply rate: 30 cm ³ / min Platen rotation speed: 45 rpm Polishing pressure: 400 gf / cm ² Polishing temperature : 25-36 ° C

Comparative Example 1 5 cm ³ of ammonia water containing 25% by weight of NH ₃ component was added to 1000 cm ^{3 of} distilled water, and the average particle size:
A colloidal silica suspension containing 20% by weight of 50 nm silica fine particles in terms of SiO _{2 of} 1.3 cm ³ was added to prepare a polishing liquid containing colloidal silica. When the pH of the obtained polishing liquid was measured with a pH meter, pH was 11.
It was 4. Using this polishing liquid, polishing was performed under the same polishing conditions as in Example 1. However, even if polishing was continued for 50 minutes, the surface of the Si wafer was not polished at all, and the surface state before polishing was maintained.

Comparative Example 2 To 1000 cm ^{3 of} distilled water, potassium hydroxide was added to 25 g of an aqueous potassium silicate solution containing 20% by weight of SiO ₂ component and 10% by weight of K ₂ O component, and the average particle diameter was 50 nm. 20% by weight of silica particles in terms of SiO ₂
Colloidal silica suspension containing: 2.5 cm ³ added,
A polishing liquid was prepared from an alkaline potassium silicate aqueous solution containing potassium silicate and colloidal silica. When the pH of the obtained polishing liquid was measured with a pH meter, pH =
It was 14. Using this polishing liquid, polishing was performed under the same polishing conditions as in Example 1. As a result, the polishing rate was 0.
It was very slow at 2 μm / min, and therefore the smoothness of the polished surface was not measured.

Example 2 1000 cm of distilled water^Three On the other hand, SiO_Two 20 layers of ingredients
% And K_Two Potassium silicate containing 10% by weight of O component
25 g of aqueous solution, NH_Three Ammoni containing 25% by weight
Oh water 5 cm^Three And the average particle size: 50 nm
SiO particles _Two Colloidal silica containing 4% by weight in conversion
Suspension: 1.5 cm^Three Add potassium silicate and
Is it an alkaline potassium silicate aqueous solution containing idal silica?
Was prepared. The pH of the obtained polishing liquid is adjusted to pH
When measured with a meter, the pH was 11.1. This
Si polishing liquid was used under the same polishing conditions as in Example 1.
The wafer was polished. As a result, the polishing rate is 0.4
5 μm / min, smoothness of polished surface is 0.7 n Ra
It was m.

Comparative Example 3 A sodium silicate aqueous solution containing 2% by weight of SiO ₂ component was ion-exchanged using an ion-exchange resin, and pH = 2.
1000 cm ³ of the silicic acid aqueous solution of 5 was obtained. Silica particles having an average particle diameter of 50 nm were added to the silicic acid aqueous solution with SiO ₂
Colloidal silica suspension containing 20% by weight in terms of conversion: 10c
m ^{3 was} added, and potassium hydroxide was further added to adjust the pH to 7.8. This aqueous solution was gelled with the passage of time and could not be used as a polishing liquid.

Example 3 Distilled water 1000 cm^Three On the other hand, SiO_Two 20 layers of ingredients
% And K_Two Potassium silicate containing 10% by weight of O component
25 g of aqueous solution, NH_Three Ammoni containing 25% by weight
Oh water 5 cm^Three And the average particle size: 50 nm
SiO particles _Two Colloidal Siri containing 20% by weight in conversion
Mosquito suspension: 1.5 cm^Three Add potassium silicate and co
Alkaline Potassium Silicate Aqueous Solution Containing Loidal Silica
Was prepared. The pH of the obtained polishing liquid is adjusted to p
When measured with an H meter, the pH was 11.1.
Using this polishing liquid, a 4-inch Si wafer was prepared under the following polishing conditions.
Ha was polished. As a result, the polishing rate is 1.0μ
m / min, and the smoothness of the polished surface is the center line average roughness (R
It was 0.7 nm in a). (Polishing conditions) Polishing device: Single-sided polishing machine with an outer diameter of a plate of 620 mm Pad (polishing): Polyurethane foam polishing liquid supply: 200 cm^Three / Min Surface plate rotation speed: 50 rpm Polishing pressure: 400 gf / cm^Two Polishing temperature: 25-36 ° C

Reference Example 1 Using a polishing slurry prepared by adjusting a pH = 11 with an alkanolamine, an aqueous colloidal silica solution having an average particle diameter of 60 nm and 2.5% by weight of silica particles in terms of SiO ₂ was used. A 4-inch Si wafer was polished under the same polishing conditions. As a result, the polishing rate was 1.1 μm /
min and the polished surface smoothness Ra was 1.0 nm.

Reference Example 2 An aqueous colloidal silica solution having an average particle size of 50 nm and 2.5% by weight of silica particles in terms of SiO ₂ was added to ammonia water (containing 25% by weight in terms of NH ₃ ) at pH = 11.4.
A 4-inch Si wafer was polished under the same polishing conditions as in Example 3 by using the polishing slurry adjusted to. As a result, the polishing rate was 1.2 μm / min and the smoothness of the polished surface was Ra of 0.8 nm.

Reference Example 3 The pH was adjusted to 10.5 by adding potassium hydroxide to an aqueous colloidal silica solution having an average particle size of 50 nm and 2.5% by weight of silica particles in terms of SiO ₂ . Using this polishing slurry, a 4-inch Si wafer was polished under the same polishing conditions as in Example 3. As a result, the polishing rate was 0.8 μm / min, and the polished surface smoothness Ra was 0.8 nm. As is clear from these results,
It is understood that by using the polishing composition of the present invention, the polishing rate and polishing smoothness equivalent to those of the conventional colloidal silica polishing slurry can be realized. Further, it is understood that the expected polishing effect is not obtained with the polishing liquid that does not satisfy the requirements specified in the present invention.

[0035]

As described above, according to the present invention, the amount of colloidal silica contained can be reduced to 1/10 or less as compared with the conventional polishing liquid which does not coexist with the water-soluble silicic acid component. Adhesion of colloidal silica abrasive grains to the polished surface
The residue can be significantly reduced, and the surface of the silicon wafer or the surface of the film made of silicon formed on the surface of the silicon wafer can be effectively prevented without causing the problems of the prior art. A polishing composition capable of polishing was realized.

[Brief description of drawings]

FIG. 1 is a graph showing the dependency of colloidal silica concentration on the polishing rate of a silicon wafer.

Claims (4)

[Claims] 1. A polishing liquid composition for silicon, which comprises an alkaline suspension containing a water-soluble silicic acid component, colloidal silica and an alkaline component and having a pH of 8.5 to 13. . 2. The polishing composition according to claim 1, wherein the content of the silicic acid component is 0.05 to 5% by weight in terms of SiO ₂ . 3. The content of the colloidal silica is Si
The polishing liquid composition according to claim 1, which is 0.005 to 5% by weight in terms of O ₂ . 4. The alkali component is alkali hydroxide,
The polishing composition according to any one of claims 1 to 3, which is one or more selected from the group consisting of alkali carbonate, ammonia, hydrazine, and organic amine.